Zener diode voltage regulator circuit



SePt- 22, 1970 R. A. ARDENGHI 3,530,367

ZENIER DIODE VOLTAGE REGULATOR CIRCUIT Filed March 7, 1969 PRIOR ARTFIG. I.

wn'NEssEs: v INVE NToR l RoberrA-G0rdenghi United States Patent O ZENERDIODE VOLTAGE REGULATOR CIRCUIT Robert A. Gardenghi, Baltimore, Md.,assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Filed Mar. 7, 1969, Ser. No. 805,131 Int.Cl. Gf 1/60 U.S. Cl. 323-8 5 Claims ABSTRACT OF THE DISCLOSURE A Zenerdiode voltage regulator circuit wherein a plurality of Zener diodes areeach connected to a respective impedance element with a like pluralityof conventional diodes connecting a load impedance across each Zenerdiode. The conventional diodes allow current to the load impedance andblock current between Zener diodes.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates generally to Zener diode voltage regulator circuits and moreparticularly relates to regulator circuits for ensuring power sharingbetween a plurality of Zener diodes.

Description of the prior art The maximum power capability of a Zenerdiode regulator is limited by the largest Zener diode available. Zenerdiodes cannot readily be connected in parallel to obtain higher powerrating unless they are precisely identical and maintained at the sometemperature. This is virtually impossible and the parallel connection ofZener diodes should be avoided.

An object of the present invention is to provide a Zener diode voltageregulator circuit allowing the attainment of virtually any high powerlevel desired.

Another object of the present invention is to provide a high powervoltage regulator circuit without the necessity of precise matching ofthe components.

Another object of the present invention is to provide a Zener diodevoltage regulator circuit of increased power capability and greaterreliability than heretofore available.

SUMMARY OF THE INVENTION The present invention accomplishes the abovecited objects and advantages by providing a plurality of Zener diodeseach connected through a respective impedance element to a voltagesource. A like plurality of conventional diodes are connected in an ORgate function to allow current to the load impedance and yet blockcurrent between Zener diodes.

BRIEF DESCRIPTION OF THE INVENTION Further objects and advantages of thepresent invention will be readily apparent from the following detaileddescription taken in conjunction with the drawing, in which:

FIG. 1 is an electrical schematic diagram in accordance with the priorart; and

FIG. 2 is an electrical schematic diagram of an illustrative embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the well knownshunt Zener regulator circuit. The current through impedance element 2is the sum of currents through a Zener diode 4 and a load impedance 6.As the magnitude of the voltage V1 at the input means varies or as amagnitude of the load impedance 6 varies, the resistance of the Zenerdiode 4 varies, thereby changing the current through the Zener 3,530,367Patented Sept. 22, 1970 ICC Vi-Vz Rs where RS is the value of theimpedance element 2. The Zener diode must be capable of dissipating thepower associated with this maximum current.

When greater power capability is desired any attempt to parallel Zenerdiodes is usually doomed because of the ditliculty in obtainingprecisely identical Zener diodes. The Zener diode which assumes all ofthe load fails when the remaining Zener diodes do not share the load.

The present allows the combining of any number of regulator circuitswithout precise matching of components. Each Zener diode 10, 12, 14 36connect each connected with a respective current limiting resistor 20,22, 24 26. Unilateral conducting means in the form of conventionaldiodes 30, 32, 34 36 connect each Zener diode to a load impedance 40.The diodes 30, 32, 34 36 allow the currents from all the regulators toflow into the load 40 and yet block the path between Zener diodes. Themaximum current that can flow in any Zener diode for a given inputvoltage V1, therefore, is determined by the magnitude of its associatedimpedance element and the Zener voltage. The conventional diodes shouldbe chosen to have similar voltage ratings and the impedance elements areto be of similar magnitude but precise matching is not necessary.

As the supply voltage V1 or the load impedance 40 is varied, thecurrents through all of the diodes will distribute according to thecomponent tolerances. The maximum current in any one Zener diode,however, will never exceed the designed maximum, no current being fed toit by the other Zener diodes. Reliable operation is thereby insured.

More specifically, as the supply voltage V1 increases from a low valueto a higher one the Zener diodes, will successively become conducting,starting with the Zener of lowest voltage break-over level. The loadvoltage will always remain between the value of the Zener which hasbecome conducting and the break over voltage of the next higher voltageZener. After the highest voltage Zener has become conducting no furtherincrease in load voltage occurs. For example, assume a circuit with only3 Zener diodes 10, 12 and 14 and that these were standard 10 volt 1-5%Zeners. The break-over voltage of any one could be anywhere between 9.5volts and 10.5 volts since they are i5% diodes. For worst case, assumediodes 10, 12 and 14 have break-over voltages of 9.5, 10, and 10.5 voltsrespectively. The circuit would then regulate for any input, V1, over9.5 volts. If V1 was greater than 9.5 but less than 10 volts, only Zener10 would break over and regulate the output to 9.5 volts. If V1 were10:3 volts, Zeners 10 and 12 would both conduct and the regulated outputwould be 10 volts. If V1 were greater than 10.5 volts all three Zeners10, 12 and 14 would break-over and the regulated output would be 10.5volts. This regulator provides a nominal l() volts since it actuallyvaries over a 5% range. Or, stated another way, the maximum amount ofregulation that can be obtained is a function of the tolerances betweenthe diodes. This is not a handicap since this circuit does have theadvantage of high power capability not obtainable otherwise.

Over the entire regulation range no individual Zener has a currentthrough it greater than where Vm is the maximum expected value of theinput voltage V1, VZ is the break-down voltage of any particular Zener,and Rs is the impedance value of a series resistor.

Changes with load resistance RL have a similar effect. Starting withRL=oo (and with V1 suiiiciently high) all Zeners are in conduction andVL-Vzm, where VZm is the breakdown voltage level of the highest voltageZener.

As RL becomes smaller and the load current increases, one by one theZeners go out of conduction and the load voltage is successivelydetermined by that Zener of the next lowest voltage level. Thiscontinues until the lowest voltage Zener goes out of conduction at whichpoint the load voltage is no longer regulated.

Thus the range of allowable load current variation has been extended bya factor of n, where n is the number of Zener diodes used.

While the present invention has been described with a degree ofparticularity for the purposes of illustration, it is to be understoodthat all modifications, substitutions, and alterations within the spiritand scope of the present invention are herein meant to be included.

I claim as my invention:

1. In a power regulator circuit the combination comprising; a pluralityof parallel circuit combinations each including a series circuitcombination of an impedance element and Zener diode; a load impedance; alike plurality of unilateral conducting means each connecting arespective common junction of said impedance element and said Zenerdiode to said load impedance.

2. The combination of claim 1 wherein said unilateral conducting meansare poled to block current between Zener diodes.

3. The combination of claim 1 further comprising an input voltage sourceconnected across each of said parallel circuit combinations.

4. The combination of claim 3 wherein said load impedance has a commonconnection to said input voltage source.

5. In a power regulator circuit the combination comprising; a loadimpedance; input voltage means; a plurality of parallel circuitcombinations serially connected with said load impedance across saidinput means, each including a series circuit combination of an impedanceelement and a unilateral conducting means; and a like plurality ofZener. diode means each connecting a respective common junction betweenan impedance element and a unilatera1 conducting means to the commonjunction between said input means and said load impedance.

US. Cl. X.R.

